Inhibition of PKC presently is believed to be one of the biochemical mechanisms by which the invented compounds produce their therapeutic effects. PKC is a family of calcium- and phospholipid-dependent serine/threonine-specific protein kinases which play an important role in cellular growth control, regulation, and differentiation. Activation of PKC has been implicated in several human disease processes including neoplasms. For example, cells transformed with the oncogenes ras,sis, erbB, abl, and src have been shown to contain elevated levels of diacylglycerol (DAG) which is believed to activate PKC. Additionally, several studies have shown increased expression of PKC in certain tumor types such as breast and lung carcinomas and activated PKC has been detected in human colon carcinomas. Further, PKC inhibitors have been reported to potentiate the antitumor activity of various chemotherapeutic agents including cis-platinum and doxorubicin.
Other human diseases in which PKC activation has been implicated include inflammatory diseases and reperfusion injury. PKC inhibitors have been demonstrated to block platelet aggregation and release of neutrophil activating agents such as platelet activating factor. PKC inhibitors also have been shown to inhibit neutrophil activation and chemotactic migration as well as neutrophil degranulation and release of proteolytic enzymes and reactive oxygen intermediates. Thus PKC inhibitors have the potential to block the most significant mechanisms of pathogenesis associated with inflammation and reperfusion injury.